Graphene represents an atomically thin layer of carbon in which the carbon atoms reside at regular two-dimensional lattice positions within a single sheet or a few stacked sheets (e.g., about 10 or less) of fused six-membered carbon rings. In its various forms, this material has garnered widespread interest for use in a number of applications, primarily due to its favorable combination of high electrical and thermal conductivity values, good in-plane mechanical strength, and unique optical and electronic properties. Of particular interest to industry are large-area graphene films for applications such as, for example, special barrier layers, coatings, large area conductive elements (e.g., RF radiators or antennas), and flexible electronics. A number of contemplated graphene applications have also been proposed for carbon nanotubes, since these two materials have certain properties that are comparable to one another. However, graphene holds an advantage over carbon nanotubes in that it can generally be produced in bulk much more inexpensively than can the latter, particularly over large surface areas, thereby addressing perceived supply and cost issues that have been commonly associated with carbon nanotubes.
Despite graphene generally being synthesized more easily than are carbon nanotubes, the form in which the graphene is produced can be problematic for certain applications. The most scalable processes for producing graphene involve depositing a graphene film on a growth substrate, most commonly a copper substrate, by chemical vapor deposition (CVD) or plasma-enhanced chemical vapor deposition (PECVD). Removing the graphene from its growth substrate can often be desirable. For example, removing the graphene from its growth substrate can often involve transferring the graphene to a secondary substrate having properties that better meet the needs of a particular application. However, graphene is often firmly adhered to its growth substrate, thereby making its removal difficult.
Conventional graphene removal processes can be problematic in many aspects, not the least of which is damaging the graphene during its liberation from the growth substrate. One way in which graphene can be removed from its growth substrate is through dissolution of the growth substrate (e.g., with an acid), leaving behind the free graphene. However, an unsupported graphene can become mechanically or chemically damaged when released in this manner. Moreover, dissolution processes can be slow, produce significant quantities of waste, and do not permit reuse of the sacrificial growth substrate. Another technique that has been used for releasing graphene from its growth substrate involves electrolytic production of hydrogen gas between the graphene and its growth substrate. Stress resulting from hydrogen bubble formation during electrolysis, although resulting in removal of the graphene from its growth substrate, can likewise produce undesirable mechanical damage within the graphene.
In view of the foregoing, improved processes for releasing graphene from its growth substrate would represent a substantial advance in the art. The present disclosure satisfies the foregoing need and provides related advantages as well.